Even if you already own a set of print-and-build dungeon walls, you’d do well to consider adding this set to your collection. The walls themselves are easy to build, but the LZW crew has included a feature I haven’t seen anywhere else: a very simple system for linking the walls together using ordinary bobby pins. That’s a great innovation. An even better innovation is the “options ruler,” which harnesses the power of PDF layers better than LZW or anyone else (as far as I’ve seen) has ever done it before. It’s a little hard to explain what the options ruler does, but once you’ve seen it in action, you’ll love the unprecedented level and ease of customizability that the system offers. This set is pretty heavy on instructions, and the instructions file credits a copy editor; while the English instructions are noticeably better than in some earlier sets, more care still needs to be taken to bring the text up the excellence of the artwork. Normally, that would limit my rating to four stars, but the excellence and utility of the options ruler overrides that this time. “E&I,” by the way, stands for “exterior and interior.”